Axial acoustic field barrier for fluidic particle manipulation (original) (raw)
Related papers
Acoustic control of suspended particles in micro fluidic chips
Lab on a Chip, 2004
A method to separate suspended particles from their medium in a continuous mode at microchip level is described. The method combines an ultrasonic standing wave field with the extreme laminar flow properties obtained in a silicon micro channel. The channel was 750 mm wide and 250 mm deep with vertical side walls defined by anisotropic wet etching. The suspension comprised "Orgasol 5mm" polyamide spheres and distilled water. The channel was perfused by applying an under pressure (suction) to the outlets. The channel was ultrasonically actuated from the back side of the chip by a piezoceramic plate. When operating the acoustic separator at the fundamental resonance frequency the acoustic forces were not strong enough to focus the particles into a well defined single band in the centre of the channel. The frequency was therefore changed to about 2 MHz, the first harmonic with two pressure nodes in the standing wave, and consequently two lines of particles were formed which were collected via the side outlets. Two different microchip separator designs were investigated with exit channels branching off from the separation channel at angles of 90° and 45° respectively. The 45° separator displayed the most optimal fluid dynamic properties and 90% of the particles were gathered in 2/3 of the original fluid volume.
Ultrasonics, 2008
The use of acoustic radiation forces for the manipulation and positioning of micrometer sized particles has shown to be a promising approach. Resonant excitation of a system containing a particle laden fluid filled cavity, can (depending on the mode excited) result in positioning of the particles in parallel lines (1-D) or distinct clumps in a grid formation (2-D) due to the high amplitude standing pressure fields that arise in the fluid. In a broader context, the alignment of particles using acoustic forces can be used to assist manipulation processes which utilise an external mechanical tool, for instance a microgripper. In such a system, particles can be removed sequentially from a line formed by acoustic forces within a microfluidic channel, hence allowing a degree of automation. In order to fully automate the gripping process, the particles must be confined to a repeatable and accurate location in two dimensions (assuming that in the third dimension they sit on the lower surface of the channel). Only in this way it is possible to remove subsequent particles by simply bringing the gripper to a known location and activating its fingers. This combined use of acoustic forces and mechanical gripping requires that one extremity of the channel is open. However, the presence of the liquid-air interface which occurs at this opening, causes the standing pressure field to decay to zero towards the opening. In a volume of liquid in proximity to the interface positioning of particles by acoustic forces is therefore no longer possible. In addition, the longitudinal gradient of the field can cause a drift of particles towards the longitudinal center of the channel at some frequencies, undesirably moving them further away from the interface, and so further from the gripper. As a solution the use of microfluidic flow induced drag forces in addition to the acoustic force potential has been investigated.
Modeling of the Acoustic Field Within Micromachined Fluidic Devices
In the last few years considerable efforts have been made to integrate acoustic fields into conventional microfluidic devices for the separation, concentration or positioning of particles [1]-[3], bringing a n important contribution to the lab-on-a-chip community. For the typical dimensions of these systems the magnitude of resulting acoustic forces are particularly well suited to the manipulation of microsized particles, such as beads and cells. An overview of the modeling of the acoustic field excited within such systems is presented here. It will be shown how a peculiar strip electrode configuration can be used to set up a standing pressure field with vertical nodal planes where particles gather, how two such fields with orthogonal wave vectors can be superimposed within a square chamber to generate a two dimensional pressure field where particles are collected in a grid-like pattern, and how the frequency of the applied signals effects the pressure field. Next, the effect of a free surface is treated, by discussing how this leads to a standing wave in the channel direction which is superimposed to the wave across the channel, resulting in one or more trapping locations within the nodal plane. The migration of particles within the pressure nodal planes themselves is analyzed as well.
We demonstrate a novel focused travelling surface acoustic waves (F-TSAW) based microchip to continuously separate microparticles, generate chemical gradient, and uniformly mix fluids inside a polydimethylsiloxane (PDMS) microchannel. Previously reported acoustofluidic based separator [1] used standing surface acoustic waves (SSAW) whereas gradient generator [2] and micromixers [3] depended on oscillating bubbles. Our microchip requires a single focusing transducer and is void of oscillating bubbles. A cumbersome microchannel alignment step, which is essential for the working of SSAW particle separator, is also eliminated. All three functions -separation, gradient generation and micromixing -are performed using high frequency F-TSAW and appropriate microchannel design.
Particle manipulation in microfluidic system using novel surface acoustic wave field
2020
This thesis examines the use of sound waves to manipulate particles in a microfluidic system for applications in lab-on-a-chip technology. Using novel acoustic fields, microscopic particles that are analogous to cells and bacteria can be sorted based on size and translocated at will within the microfluidic system. This technology could be used to improve the accessibility and affordability of medical diagnostics and monitoring.
A detachable acoustofluidic system for particle separation via a travelling surface acoustic wave
Analytical chemistry, 2016
Components in biomedical analysis tools that have direct contact with biological samples, especially bio-hazardous materials, are ideally discarded after use to prevent cross-contamination. However, a conventional acoustofluidic device is typically a monolithic integration that permanently bonds acoustic transducers with microfluidic channels, increasing processing costs in single-use platforms. In this study, we demonstrate a detachable acoustofluidic system comprised of a disposable channel device and a reusable acoustic transducer for non-contact continuous particle separation via a travelling surface acoustic wave (TSAW). The channel device can be placed onto the SAW transducer with a high alignment tolerance to simplify operation, is made entirely of polydimethylsiloxane (PDMS), and doesn't require any additional coupling agent. A micro-structured pillar is used to couple acoustic waves into the fluid channel for non-contact particle manipulation. We demonstrate the separat...
Journal of Fluid Science and Technology, 2009
A non-intrusive and continuous separation technique for suspended particles in a microchannel has been developed by utilizing acoustic radiation force with two ultrasonic transducers. The technique has two major advantages that the acoustic radiation force acts on particles in proportion to particle diameter, and collects particles to the nodal positions of the standing wave field perpendicular to the flow direction. Thus the large size particles have shorter time of transfer to the nodal positions than the small size particles. Particle velocities toward the nodal position within the sound field were measured by particle tracking velocimetry, and both the migration times of particle transfer to the nodal positions and the acoustic radiation force were evaluated from the particle images and velocity data in order to separate particles in the flow field. The ultrasonic transducers with 5 and 2.5 MHz were equipped parallel to the flow direction. Both large and small particles in the aqueous solution were trapped at the nodes of the upstream in 5 MHz sound field, and 2.5 MHz transducer was radiated to move only large particles toward a nodal position of its sound field. The exposure time of 2.5 MHz transducer was determined from the migration times of large and small particles transfer to the nodal positions. It is confirmed that the continuous and selective separation based on particle diameter was accomplished by the present technique.